Liskov Substitution and Modularity in Network Design
Furthering the thoughts I’ve put into the forthcoming book on network complexity…
One of the hardest things for designers to wrap their heads around is the concept of unintended consequences. One of the definitional points of complexity in any design is the problem of “push button on right side, weird thing happens over on the left side, and there’s no apparent connection between the two.” This is often just a result of the complexity problem in its base form — the unsolvable triangle (fast/cheap/quality — choose two). The problem is that we often don’t see the third leg of the triangle.
The Liskov substitution principle is one of the mechanisms coders use to manage complexity in object oriented design. The general idea is this: suppose I build an object that describes rectangles. This object can hold the width and the height of the rectangle, and it can return the area of the rectangle. Now, assume I build another object called “square” that overloads the rectangle object, but it forces the width and height to be the same (a square is type of rectangle that has all equal sides, after all). This all seems perfectly normal, right?
Now let’s say Continue reading
